Process for separating chlorodiphenyls



Patented Dec. 6 1932 UNITED STATES.

PArE roF icEY j EDGAR o. BRITTONAND WESLEY c. sronssnnjonM1nLAnn,"1vrIcHIGAN, Ass IGiTons 7 To THE DOW CHEMICAL COMPANY, onMIDLAND; MICHIGAN, A oonrona'rron or MICHIGAN Pnoonss ironSEPARATINGCHLQRODIJPHENYLS 5 Application filed December 22, 1930. Serial1101503338.

This invention is concerned with the separation of ,orthoandpara-monochlorodiphenyls from a mixture containing the: same, especiallywith a process forobtaining separately the several components from aproduct formation of dichloro compounds, thechloa rination should becarried only to a point where considerable diphenyl remainsunchlorinated, which'must be separated from reaction product. Thisreaction mixture may 3 be separated to some extent into its componentsby repeated fractional distillation thereof. The separation of theaforesaid fractions into their constituents is difficult in View of therespective boiling points thereof, namely, diphenyl, 254.9 0.;ortho-ch1oro-' diphenyl, 268? (l; para-chlorodiphenyl, 282

0.; and meta-chlorodiphenyl,2848-2859 G..

if present. To accomplish this separation, fraotionating equipmentcapable of very accurate control is necessary; However, such a procedurehas notresulted satisfactorily in a practical way because of thenumerous" repetitions of such fractionation required and because oftheresulting low yield of purified product obtained fromjeach'suchfractionation. Furthermore, the degree of control demanded is notreadily obtainable in a commercial process. p

We have now found .that the aforesaid chlorinated mixture mayadvantageously be separated into its components by .an improved process,combining both fractional distillation and crystallization steps, whichrequires merely an ordinary degree of control. \Ve first distill'toseparate into fractions, one fraction containing the unreacted diphenyland part of the ortho-chlorodiphenyl practically free from thepara-isomer,

procedure whereby the v'ention may be used.

' our process,"

and the other fraction containing substantial ly all of thepara-chlorodiphenyl together I with the remainder-of. theortho-compound. I

Such fractions maythen-be separated into then components bycrystallization under suitable conditions, theindividual compoundsbeingobtained thereby substantially pure and in satisfactory yield; Bythis improved methodof separationweare ableito purify either of theaforesaid compounds asdesired v to obtain such-purified products as aredemanded in tl1e"dye,plastic, pharmaceutical,

and other allied industries,- Accordingly, our inventlon resides in thesteps hereinafter fully described and particularly pointed out theclaims, the annexed drawings and following description setting forthjindetail certain In said annexeddrawings containing diphenyl' andorthoichlorodiprinciple of our in- V v I. him. The charts thereappearing show, respectf1vely,the freezing point curves of mixturesphenal in Fig. I and orthoand p'a' ra-chloro i diphenyls'in Fig; II. Fig; III is a flow sheet nterconnected andrelated stepsj in ourimprovedprocess;

' The reaction mixtureconsisting of diphenyl and chlorinated diphenyljsto be separated by our improved method is conveniently ob l9 29'now-Patent' No. 1,835,751. Example III of such applicationisparticularly "applicable to the present'purpose; however, in place ofdiagrammatically illustratingthe sequence of benzene we preferablyemploy chlorobenzenej as a solvent. A typical reaction mixture afterdistilling off the solventptherefore, for example, may consistlofil to30 percent of unreacted di phenyl,-25to40 per cent ofortho-jchlorodi'phenyl and25to4O percent offpara chlorodiphenyhand a residue of5 to ;20 per 7 cent. of higher chlorinated diphenyl derivatives,principally dichlorodiphenyls, which} 7 are crystalline. present.

To illustrate the I crystallization phase. of

charts showing the freezing Tarrymaterials may also- 1 points ofmixtures comprisin the two frac- 'para-chlorodiph'enyls. V 7

III of the'drawing's, the sequence of steps is shown diagrammatically, j

itica'lly equal proportions, is cooled to about tions are given. Asshown in l ig. I by cooling a given mixture of diphenyl. andorthochlorodiphenyl'to approximately 19 C. an

eutectic composition containing approximately I 68.4 per centortho-chlorodiphenyl and 31.6 percent'diphenyl is obtained. In

II a mixture of orthoand'para-chlorodiphenyls, when cooled to about 13C.,fgives an eutectic composition made upof approxiniately' 70 per centortho-' and -per cent Referring to Fig.

the order of the movementjof materials and intermediate products beingindicated :by. the

arrows. Beginning with the aforementioned 'reacti'onmiXt-ure, the sameisfirst made alka line, e. g.,by' addition ofllaOH or Na CO to removehydrogenchloride therefrom and I then fractionally distilled to preparethereby successive fractions consisting; substantially (1)"solvent,(2.1g. chlorobenzen-e, which.may

be returned to thefchlorinating process;

- diphenyl'and ortho-chlorodiphenyl; or-

thoand para chlorodiphenyls; includingany' I of the meta isomer; ifpresent; and leaving a residue'of 5' to 20. per cent of the originaltemperature of about 260to274 (lat which said fraction may containapproximately equal amounts of diphenyl and ortho-chlo'rodiphenyl. Theseproportions maybe obtained without'any appreciable amount of thepara-..,

volume, such residue comprising amixture of poly-.chlorodiphenyl's. and"tarry 'materialQ After removing the first fraction containing.

the'solv'ent, the second fraction is taken at a chlorodiphenyldistillingover. By furth er distillingfat a temperature'of about 27 i? to 284C.'the remaining ortho chlorodiphenyl and practically all of thecorresponding paracompound are obtained in the third fraction.

. I To divide fraction (2),as. designated v in Fig. III, the same ispreferably cooledto a temperature between 199'a-nd 25?,' G.,"'e. g apoint slightly above the eutectic as shown in F ig..I, whenias much as30fper-ce'nt ofdiphenyl {crystals are formed; which may," be.c'entrifi'iged or otherwise separated from the mixture, the temperatureof the mother liquor being. such as to maintain the diphenyl V incrystalline form." The above eutecticresidue mother liquor; "whichcontains from about to 7 0. per cent'of orth'o chlorodiphenyland v 11035per cent diphenyl, is now distilled'at a temperature between about256and 260 C. to. obtain a fraction containing about equal proportions ofdiphenyl andortho-chlorodiphenyl, which is returned to the original;v(2) I fraction mixture. The stillfresidue'from the above. distillation;which mayfcontain upw wards offper cent of the ortho-comvpound cent oforthoandfthe remainder parachloroe.

that may contain. about elqual partsQofjthe preferred Way of'carrying'out the various steps of our process I f and 50 per centortho' clilorodiphenyl tilled, thereby obtaining 434 grams of a n anidijortlio-dichl due obtained therefrom may then be returned to one of thecrude intermediate fractions,

as shown. It may be advantageous in certain instances to dissolve theabove still residue in. a suitable solvent, e. ;g-. ethyl alcohol,methyl alcohol, etc., andi zthenfiseparate the orthochlorodiphenyltherefrom by cooling the mixture. The procedure for separating 'thesodesig nated fraction is generally similarto that just described." iThisliquid fraction; which may contain the orthoand para-chlorodiphenylsin prac so 13 to 17? 0., e.; g.,apointslightly above: the eutectic asshown inFig. II, when substan. tially pure crystals ofpararchlorodiphenyl are formed and are centrifuged or otherwise;removed..f1o1 n the mother.liquoigfeBy-l peated cooling thel para isomermaybetO large extent removed. fromj the mother liquor; except, ofcoursefthat requireclitoform I eutectic mixture, which; contains. thevicin- 'miXture-may, now be distilled a tempera; 'ture range of about275. to; 278 being.

most suitable, and the fraction thus obtained; which: mayicontain even.in excess f of .90. per.

diphenyl, may further cooled, pri-zferably toabout 139 ,G. asemployed'ina former step v whereby practically pure forthoi-chlorodi i phenylisobtained. and is separated as pre. viously'described. Here also, asinfraction (2 itJmay'b-e of advantage to'crystalliactheorthoand"para-chloro diphenyls from e917, vent. The residue from thelastdistillation,

ortho- Ia'nd. para isomers; is returned to the former step as showninFig. IILeud maybe reworkedfwith subsequent. fr on. By

this method eve-tau of the original rniziture may he resolvedintoitspurefconsti'tucntsjin 1 a single cycle. j

[The following ex 'a nipleswillj illnstratea V .-';Emamplel 7AmiXtureofLlQQQ o f th eliquid-flats tron conslstingof aboutb'Q per centdiphenyl which has a freezing jmintof 5 0.5 oi.

cooled to 20, C. 268 gramsofdiphenyl tals .Were.., ,separated.outleaving a liquid.

} residue. containing. app'ro'i iiniately .68} per I centortho-chlorodiph'enyl a d;s1, e; er cent diphenyl. "Theoily residue wasnow dis ture of about. equal mo was in :excess' 0i195 percent ofortho-chlorodi.- phenyl. By coolingthe ortho-chlorodiphe nyl mixturejust separated to approximately 0., 1 gramsof'practically pureortho-chlorodiphenyland 47 grams of the eutectic mixture remaining wereobtained,:

the latter of which was returned to the oily residue in the former stepand redistilled as there described.

Ewamiple I I 900 grams of a mixture consisting of about equal amounts ofthe orthoand para-chlorodiphenyls, and which has a freezingpoint ofabout 37 C. was cooled to around 13 C.

whereby crystallization was induced and j grains of thepara-isomercrystals separated out leavlng a liquid eutectic residue containingapproximately per cent of the orthos and 30 per cent of the parachlorodiphenyls. Saidresidue was now distilled whereby there wasobtained 285 grams of a mixturecontaining in excess of per cent:ortli'o'-chlorodiphenyl, and a residual solution chi-3 58 gramsconsisting of orthoand para-chlorodiphenyls innearly equal 'proportions,which was returned to the first step of the present separation. Theortho-chlorodiphenyl mix ture above was nowcooled to approximately 13 C.and filtered, thereby obtaining '23? grams of pure ortho-chlorodiphenyland'fi' V grams of the eutectic mixture, e. g. containing about 70'percent orthoand 30 per cent para-chlorodiphenyls, the lattl3j0f which wasreturned to the liquid eutectic residue of similar composition in aformerstep.

It is noted that se'edingout or other well known manipulation may beresorted to in removing the possibility of forming crystals of theeutectic mixture which would be removed along with the pure productdesired, thuscontaminatingthe same. j

: Althoughour improved" method is generally applicable to the separationof the V II L'two fractions, there designated as (2): and (3) ;are'obtained. If, however, the mix ture-contains largely only diphenyl and'orthoand paraemonochlorodiphenyls from mixtures containing the same,yet when an excess of diphenyl is needed incarrying out the chlorinationstep and is therefore present in'the mixture with the isomers, in suchinstance the'separation of the diphenyl from said isomers becomesanessential partof the process. tially only three components contains inaddition a solvent, distillation will be the first step, by meansofwhich the solvent will be removed as fraction (1), and in the twosuc-.

cessive distillationsteps as illustrated in Fig;

7 For the m xture it will be seen by inspection of Fig. I that 1f suchmixture contains the d1- If the above mixture of substanortho-chlorodiphenyl, or orthoand parachlorodiphenyls, either coolingordistilla tion may be the first step, depending upon the proportions inwhich they existin the mixture. i r

5 diphenyl-ortho-chlorodiphenyl phenyl constituent inuless than theeutectic ratio, cooling will be in orderto-separateorthoechlorodiphenylw crystals in "a motherliquor of: diphenyl andortho-chlorodiphenyl, whereas itthe diphenyl is present in proportiongreater thanthe eutectic ratio, cooling will be practiced to separatediphenyl crystals; but, .ifagain, the constituents be present in,-orapproximately in, the eutectic ratio, then distillation will be thefirst step bymeans ofwhich. the bulk ofthe ortho will be concentrated inthe residueafter removal of a flEtCtlOIICOiltflllllflg the bullr of the'di-U phenyl, This" residue will then i-be cooled; to

produce ortho-chlorodi'ohenyl crystals-and ail-eutectic mother liquor;

With mixtures containing orthoand'para chlorodiphenyls, inspection ofFig: Ilwill show that ii the para isomer be present in proportion less.than that representing a eutectic mixture, cooling will 'bev practicedtoseparate outorthocrystalszin ainother liquor oforthoandipara-chlorodiphenyls. If, how f ever, the para'isemer bepresent in propor= tion greater than that repres entinga eutecticmixture, cooling wil'l be'practiced toseparate' out para chlorodiphenylc rystals,and, again,

ifthel constituents are present in, orapproximately 1n, the eutecticratio, distillation will be practiced first to concentraterthe orthoisomer in the distillate: and return the bulk of the para isomer in theresidue to a previous step. The fraction thus obtained, hi gh inortho-chlorodiphenyl; will then be cooled to separate ortho crystals andthe eutectic residue mother liquor. returned to a previous step. i

. 110. It will thus be seen that byalternate applia cation of the stepsof cooling and distillation, or distillation'and cooling, as thecomposition may dictate, the'para and orthoemonochlorodiphenyls maybeseparated from a mixture' diphenyl maybe separated from a mixturethereoffand, further, that ifin the originah mlxturea solvent bepresenta preliminary distillation may be practiced to eliminate it; as thefirstdistillata either from an original I mixture containing diphenyland ortho-chlorodiphenyl, diphenyl, 'orthoand para-chlo- I rodiphenyls,:or ortho-"and para-'chlorodi-q Y i phenyls; together with the solvent.

In the foregoing, we have described a prfo cedure for separatinga'mixture'ofdiphenyl,

orthoand para-'chlorodiphenylsasobtained by the chlorination ofdiphenyl, butthe mix! ture' may be-derived in other fways and with? 1'15thereof and the-adiphenyliand Ortho-chlOro- Hvarying proportions of the.constituents thereof. We, have carried out the fractionation steps ofour improved process under reduced pressureand a corresponding reducedtemperature. as well as under normal pressure with an equallysatisfactoryseparation. Our improved process, or certain of the stepstherein, may be further employed for purifyinglthe individual compoundsor. for separating mixtures of two or more-of them.

7 Other modes of applying the principle of our invention may be employedinstead of theone explained, change being made as re 7 gards thedetails, provided the step or steps distin'ctly'claim asourinvention:.- 1. The method of separating ortho-chlorodiphenyl andpara-chlorodiphenyl from a {stated by any of the following claims orequivalent thereof be employed;

lVe therefore particularly pointout and mixture containing the same innon-eutectic proportion which comprises the step of pre cipitating oneof said compounds-as crystals from the liquid mixture by cooling to atemperature approximating, but not .lower than i the eutectic freezingpoint.

2.: The, methodof separating I diphenyl j and para-ohlorodiphenylitrom amixture containing the same innon 'eutectic proportion wh ch comprises.the steps of precipitating one of said compounds ascrystals sistingchiefly of ortho-chlorodiphenyl and V ing point. 7 r 4'. The method ofseparating diphenyl and ortho-chlorodiphenyl froma mixture confromtheliquid mixture by cooling to a temperature approximating, but not'lowerrthan theeutectic tt'reezing point, and then distilling the motherliquor to separate a fraction conleave aresidual mixture containing asubstantially higher proportion of para-chloro diphenylthanicorresponds' to: the eutectic mixture." p

:3. The method of separating diphenyl and orthoechlorodiphenylfrom amixture containing, the same in non-eutecticproportions which comprisesprecipitating one of said compounds as crystals from the liquid miX-turerby cooling to a'temperature approximating, but not lower thanthe-eutectic fr'eez taining. the same in non-eutecticproportionswhichfcomprises precipitating one of said compounds as crystals from theliquid mixture by cooling to a temperature approxii Imating, but notlowerthan the eutectic freezfling pointpand then distilling the motherliquor toseparate a fraction containing a sub diphenyl, I

stantiallyhigher proportion of diphenyl than corresponds to the eutecticmixture and leave a residue consistingv chiefly of DI thO-Cl'llOI O- V5. In a method-of the character described,

the stepswhich consist in separating diphenyl 1 from a'mixturecomprisingmono-chlorodi- 'w'phenyls and diphenylby, distilling saidmix-' ortho-chloro- V ture to obtain a fraction consistingfof-di' phenyland ortho-chlorodiphenyl in ,{noneutectic proportions and crystallizing'd1: phenyl from said fraction. 1

6. "In a method of the character described;

the'steps which consist in crystallizingdie V phenyl from a mixturethereof with -rthochlorodiphenyl in non-eutecticproportions untilapproximately an eutectic mixture. of the compounds is formed andseparating the diphenyl crystalsfrom the liquid eutectic mixture. 7 a

., 7 Ina method of the character described,

the steps which consist in crystallizing 'diphenyl from a mixturethereofwith orthochlorodiphenyl in non-eutectic proportions by cooling to atemperature of approximately 19 to C. until approximately an eutecticmixture of the compounds is formed and s ep-, arating the diphenylcrystals from the liquidi eutectic mixture.

- 8. In a method of thecharacter l the steps which consist incrystallizingortho-f chlorodiphenylfrom a mixturecomprising 5 o;

ortho-. and 'para-chlorodiphenyls gin non: v

. eutectic proportions until approximatelygan,

eutectic mixture .ofthecom pounds is formed,

removing crystals of ortho-compound, .and

" separating para-chlorodiphenyl by distilling I the same from saideutecticvmixture; V

9. In a method for thepurificationoforthochlorodiphenyl the steps whichconsist of ing the crystals ofortho-chlorodiphenyl, and

separating para-chlorodiphenyl by distilling the same from the residue.r

10; The method of vseparatinglamixture V consisting of diphenyl,ortho-chlorodiphenyl V and para-chlorodiphenyl into the componentsthereof, Which comprises separating said mix-- ture by distillation intoa fraction consisting of diphenyl and ortho-chlorodiphenyl in non- 7eutectic proportions and another fraction consisting of orthoandpara-chlorodiphenyl,in non-eutectic proportions,and then separating bycooling each fraction into its components.-

"11. The method of separating a mixture 7 consisting of diphenyl,'ortho-jchlorodiphenyl V and para-chlor0diphenyl ;into-,,the rcomponentsthereof, whichv comprises, separating o said mixture by distillation,into a fraction;

consisting substantially of diphenyl and ortho-chlorodiphenyl innoneeutectic proportions and another fraction consisting T of orthoandpara-chlorodiphenyls in none eutectic proportio-ns,'separating saidlfirstl fraction. by, crystallizing'v-out, diphenyhby; I

cooling, removing the crystalsifromthe liqiiidf residue and distillingthe latter to Obtain a;

distillate consisting substantiallyof'diphenylf 1 36 andortho-chlorodiphenyl and a still residue consisting largely ofortho-chlorodiphenyl, crystallizing para-chlorodiphenyl from said secondfraction by cooling, removing the crystals from the liquid residue anddistilling the latter to separate a fraction consisting substantially ofortho-chlorodiphenyl therefrom. q

12. The method of separating a mixture consisting of diphenyl,ortho-chlorodiphenyl and para-chlorodiphenyl into the componentsthereof, Which comprises separating said mixture by distillation into afraction consisting of diphenyl and ortho-chlorodiphenyl in non-eutecticproportions and another fraction consisting of orthoandpara-chlorodiphenyls in non-eutectic proportions, separating said firstfraction by crystallizing out diphenyl by cooling to a temperature ofabout 19 to 25 0., removing the crystals from the liquid residue anddistilling the mixture of the above mentioned compounds, and the secondof which contains parachlorodiphenyl in a proportion greater than thatpresent in an eutectic mixture of the two isomers, and cooling each ofsaid fractions ma temperature approximating, but notlovver than theeutectic freezing point, where by ortho-chlorodiphenyl is crystallizedfrom the first fraction and para chloro'diphenyl is crystallized fromthe second.

a EDGAR o. BRITTON.

WESLEY o. STOVESSYER.

latter to obtain a distillate containing prac tically all the remainingdiphenyl and a portion of the ortho-compound leaving a residueconsisting substantially of ortho-chlorodiphenyl, crystallizingpara-chlorodiphenyl from said second fraction by cooling to atemperature of approximately 13 to 17 0., removing the crystals from theliquid residue and distilling said residue to obtain a distillateconsisting substantially of ortho- V chlorodiphenyl.

13. The method of separating a reaction mixture from the chlorination ofdiphenyl wherein mono-chlorinated diphenyls are the principal products,Which comprises distilling said mixture to obtain a fraction consistingsubstantially of 'unreacted diphenyl and ortho-chlorodiphenyl innon-eutectic proportions and another fraction consisting of orthoandpara-chlorodiphenyls in noneutectic proportions leaving a still residueof poly-chlorodiphenyl compounds, separating said first fraction bycrystallizing out diphenyl by cooling to a temperature of about 19 to 250., removing thecrystals from the liquid residue, distilling the latterto obtain a distillate containing practically all of the to obtain tWofractions,.the first of which 7 contains ortho-chlorodiphenyl in aproportion greater than that present in an eutectic Signed'by us this17th day of December,

